Seven Wonders of the World: Old and New

There are many amazing things in the world, but it is not so easy to earn the honorary title of "wonder of the world." The Great Pyramid of Giza, the Great Wall of China, the Colosseum - each of these structures is considered one of the wonders of the world, and you have probably heard of them. But why are they called that? How do the old wonders of the world differ from the new ones? And why are there exactly seven of them?